After this date only security fixes will be provided for SharePoint 2010. That means if you are running into an issue after October 13th which is caused by a problem in SharePoint 2010 and which has not already been addressed before you will no longer be able to request a hotfix.
Not the best situation if you are using SharePoint 2010 as a business critical application.

There are still three months till deadline – enough time to evaluate SharePoint 2013 and consider an upgrade.

In here ; SharePoint is telling you that it cannot find the Workflow Manager service endpoint at this address
– Check for the Firewall and possible networking issues.
– Make a browser test that you can browse the workflow host uri
-Check the WFM IIS for the bindings of the Workflow Manager Site
-Check that the workflow manager IIS to make sure that the Workflow Manager Front End is running on correct port !.

You can face this because App Management Service application is not provisioned or the App Management Service is not running or the App Management Service Proxy is not added to the default proxy group.
-Check the app management service from CA -> Application Management -> Manage Service Application . If it is not provisioned , provision it.

Then if you face this ;
Microsoft.SharePoint.SPEndpointAddressNotFoundException: There are no addresses available for this application.
at Microsoft.SharePoint.SPRoundRobinServiceLoadBalancer.BeginOperation()
at Microsoft.SharePoint.Administration.SPServiceApplicationProxyBase`1.ExecuteOnChannel(Boolean requireDelegation, Action`1 codeBlock)
at Microsoft.SharePoint.AppManagement.AppManagementServiceApplicationProxy.GetScaleOutDatabaseMap()
at Microsoft.SharePoint.SPScaleOutDatabaseMap.GetMapCacheEntries

-Dont forget to start App Management Service from CA-> Services on Server -> App Management Service
–Make an IISReset

When you try to run a SP 2013 workflow, you get a ‘suspended’ error message, and the error states;
RequestorId: <Guid>. Details: RequestorId: <Guid>. Details: An unhandled exception occurred during the execution of the workflow instance. Exception details: System.ApplicationException: HTTP 401 {“error_description”:”The server was unable to process the request due to an internal error.

The reason may the security service application is unable to identify the user id from the user claim

Content type Publishing will include workflow associations, but not the workflow themselves. It is by design , In SharePoint 2010, Content Type Publishing will include the workflow association, however the actual workflow is not published. To work around this behavior, workflows should be manually created or transferred to the site before the Content Type and workflow association are published.

First check that the state service Application has started and State Service Application Proxy has been assigned to your web Application ;

Open your Central AdministrationGo to Application ManagementUnder Service Applications click Configure service application associationsClick on the Application Service Proxy Group of the WebApplication you’re trying your workflow on
Find State Service Application and make it checked .

If you dont have State Service Application you can create a new one by below;

1. Click and lunch Start->All Programs -> Microsoft SharePoint 2010 Products-> SharePoint 2010 Management Shell .
2. In Windows PowerShell, type $stateapp= New-SPStateServiceApplication -Name “State Service Application”3. Create a State Service database and associate it with a service application, by typing New-SPStateServiceDatabase -Name “StateServiceDatabase” -ServiceApplication $stateapp
4. Create a State Service Application Proxy and associate it with the service application by typing New-SPStateServiceApplicationProxy -Name “State Service Application Proxy” -ServiceApplication $stateapp -DefaultProxyGroup

“SharePoint 2010 Server stops working after installing KB 2756920”
“Problems with SharePoint 2010 Server after installing Windows Updates, like – Errors in the navigation panes – Complete failure to open any site – SharePoint sites will return 503 server error.When you check the Server’s Event- and/or ULS logs, you may find some errors similar to these:

Sender Information: System.ServiceModel.ServiceHostingEnvironment+HostingManager/17653682Exception: System.ServiceModel.ServiceActivationException: The service ‘/SecurityTokenServiceApplication/securitytoken.svc’ cannot be activated due to an exception during compilation. The exception message is: Method not found: ‘System.String System.ServiceModel.Activation.Iis7Helper.ExtendedProtectionDotlessSpnNotEnabledThrowHelper(System.Object)’.. —> System.MissingMethodException: Method not found: ‘System.String System.ServiceModel.Activation.Iis7Helper.ExtendedProtectionDotlessSpnNotEnabledThrowHelper(System.Object)’.”

If you have a bull headed Enterprise Search Service Application and you can not able to delete this service application by Central Administration or fallowing powershell script
$ssa = Get-SPServiceApplication -name “<Search Service Application Name>”
Remove-SPServiceApplication $ssa

The symptoms is when you attempt to delete this service application powershell or web GUI is hanging until timeout.

So you may try fallowing powershell command to force to delete:

1) Open the SharePoint PowerShell on the SharePoint server and run the following commands:
2) Run fallowing command which will list all Enterprize search applications and their GUIDsGet-SPEnterpriseSearchServiceApplication
Take note of problematic service application guid
3) Type fallowing command:$ssa = Get-SPEnterpriseSearchServiceApplication -id “<noted guid here>”
$ssa.unprovision(1)

if the above command is successful the SSA will be deleted, if it is hung, then try fallowing:
1) Open a new PowerShell:
2) Run fallowing command which will list all Enterprize search applications and their GUIDsGet-SPEnterpriseSearchServiceApplication
Take note of problematic service application guid